Arrangement in a pipe joint for a heat exchanger

ABSTRACT

Pipe connection for heat exchangers ( 1 ) having a number of corrugated plates, where each plate has a first edge part opposite a second edge part and a third edge part opposite a fourth edge part, between which corrugated plates there are provided first and second flow channels. A heat-emitting medium ( 6 ) flows through every alternate channel and a heat absorbing medium ( 7 ) flows through every other alternate channel. A collecting channel ( 8 ) is provided having a diverging cross-section for the heat-emitting medium ( 6 ) and is placed at one side of the heat exchanger and connected to an inlet section of a combined inlet and outlet pipe joint ( 2, 3 ) for the heat emitting and heat absorbing media. An outgoing collection channel ( 4 ) for the heat-absorbing medium ( 7 ) is arranged on the same side of the heat exchanger and connected to an outlet section of the inlet and outlet pipe joint ( 2, 3 ). The inlet pipe joint ( 2 ) includes a deformable first pipe section ( 10 ), arranged to absorb thermal and mechanical loading in both axial and radial directions, and at least one further, second pipe section ( 2   a   , 2   b ).

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation patent application ofInternational Application No. PCT/SE02/00959 filed 17 May 2002 which waspublished in English pursuant to Article 21(2) of the Patent CooperationTreaty, and which claims priority to Swedish Application No. 0101797-9filed 21 May 2001. Both applications are expressly incorporated hereinby reference in their entireties.

BACKGROUND OF INVENTION

[0002] 1. Technical Field

[0003] The present invention relates to an arrangement in a pipe jointfor a heat exchanger also termed a recuperator that is adapted for usewith a gas turbine for stationary use in a small scale combined powerand heating plant or for mobile use in a vehicle.

[0004] 2. Background Art

[0005] A heat exchanger of the type may be used in, for example, acombined power and heating plant, for mobile use or in a reserve powerstation. For many such applications it is of vital importance that therecuperator is designed in such a way that is as efficient as possible,while minimizing weight and dimensions. The recuperator may, forinstance, be made up of a plate heat exchanger comprising a number ofplates manufactured from very thin sheet metal, generally having athickness of about 0.1 mm. The plates are provided with corrugations ina known manner, whereby they are stabilized relative to each other in awave shaped pattern. Spaces between the corrugations will then form flowchannels for a heat emitting medium and a heat-absorbing medium. If agas turbine is used, the heat-emitting medium is combusted gases leavingthe turbine, while the heat-absorbing medium is usually air.

[0006] As the heat emitting and absorbing media may have a relativelyhigh temperature, problems may arise in tubing and pipe joints of suchsystems. When starting a plant using a gas turbine, the temperature inthe component parts will rise from ambient temperature, for example 20°C., to temperatures in excess of 600° C. This usually entails largethermal loading due to heat expansion in different parts of the system.In operation the variations in temperature between different parts ofthe plant are less, but may still cause problems.

[0007] At pipe joints between two sections of a heat exchanger, orbetween a source of heat and the heat exchanger, for instance between agas turbine having exhaust gases requiring cooling, it may therefore benecessary to absorb forces that arise due to the fact that the heatexchanger packet and the pipe joint are very likely to have differentcoefficients of heat expansion. For this reason, welded or solderedjoints in pipe systems without the capability of absorbing thermalloading are totally unsuitable, as repeated thermal loading will quicklygive rise to cracks and leaks. Corresponding problems will also ariseshould mechanical joints, such as bolted connections, be used.

[0008] One solution, though deficient, is shown in FIG. 2 that includesan inlet pipe connection 2 for conducting a heat emitting medium 6 tothe heat exchanger. According to this example, the combusted exhaustgas, at a temperature of about 650° C. and a pressure of about 1.1 bars,is conducted from a gas turbine to the inlet pipe connection 2 and intothe heat exchanger. In the heat exchanger, a heat absorbing medium 7,such as air, is heated by the exhaust gases, whereby the air leaves theheat exchanger through the outlet pipe connection 3 at a temperature ofabout 610° C. and a pressure of 4 bar. The lower end A of the inlet pipeconnection 2 is mounted with a force fit onto a corresponding recess ina flange on the heat exchanger. The lower end A can be provided with anumber of radial grooves C around its periphery, in order to increasethe contact pressure between said end and the recess B. The grooves Cmay also be provided with sealing devices of suitable kind. Thermalloading caused by, for instance, axial expansion of the inlet pipeconnection must be absorbed by the joint, therefore the component partsmust be movable relative to each other.

[0009] In addition to its sensitivity to uneven loading, both during andafter assembly, the arrangement may also have a certain leakage flowL_(F) between the inlet and outlet parts. The leakage flow is partly dueto the pressure difference and partly due to poor fitting and relativemovement between the component parts. Such a leakage will lower theefficiency of the heat exchanger.

[0010] Hence one problem is to achieve a pipe joint that can be deformedin order to absorb thermal loads without being damaged. Depending on thepositioning and assembly of the pipe joint, it may have to absorbmovement in both axial and radial direction, in relation to the mainaxis of the pipe joint.

[0011] A further problem is the fit of such a pipe joint between twofixed points, where variations in fit and tolerance between thecomponent parts of the heat exchanger may sometimes occur. In such casesit is also desirable to have a pipe joint that is deformable in severaldirections.

SUMMARY OF INVENTION

[0012] The purpose of the current invention is to eliminate problemsassociated with known solutions, thereby fulfilling the desiredobjectives of an improved pipe arrangement for a heat exchanger, as wellas providing a simple and inexpensive arrangement for this purpose.

[0013] The purpose(s) of the invention are achieved by means of a pipearrangement for heat exchangers and relating to pipe joint(s) for theheat exchanger which comprises (includes, but it not limited to) anumber of corrugated plates. Each plate has a first edge part opposite asecond edge part and a third edge part opposite a fourth edge part.Between the corrugated plates there are provided first and second flowchannels, where a heat emitting medium flows through every alternatechannel and a heat absorbing medium flows through every other alternatechannel. A collecting channel for heat emitting medium, which channelhas a diverging cross-section, is placed at one side of the heatexchanger and is provided with an inlet section connected to a combinedinlet and outlet pipe connection for the heat emitting and heatabsorbing media. In addition, an outgoing collection channel for theheat-absorbing medium is arranged on the same side of the heat exchangerand has an outlet section connected to the inlet and outlet pipe. Theinlet pipe comprises a deformable first pipe section, arranged to absorbthermal and mechanical movements in both axial and radial directions,and at least one further pipe section. The deformable section ispreferably, but not necessarily, elastically deformable. According toone embodiment, the heat exchanger can co-operate with a gas turbine,whereby its combusted exhaust gases are used as the heat-emittingmedium.

[0014] According to a one embodiment, the inlet pipe connection has adeformable first pipe section made up of a substantially cylindricalpipe, with walls having a corrugated cross-section in the axialdirection of the pipe. Such an embodiment can as a rule entail certainflow losses. In order not to limit or disturb the flow through the pipejoint, the average diameter, that is the average of the inner and outerdiameters of the corrugations, should be larger than the inner diameterof the adjoining second pipe section. Preferably, the inner diameter ofthe deformable first pipe section, corresponding to the smallestdiameter of the corrugated section, is equal to the inner diameter ofthe second pipe section. The cross-section of the corrugated section maybe varied depending on the size and direction of the thermal movementsto be absorbed. One example of a suitable shape is a sinusoidalcross-section, where the amplitude and wavelength can be varied to givethe desired properties with respect to deformability in the axial andradial directions. The first pipe section is preferably elasticallydeformable.

[0015] According to an alternative embodiment, where the inlet andoutlet pipe joints are arranged concentrically, it is further possibleto distribute the flow losses between inlet and outlet. In this case,the average diameter of the corrugated section, that is the average ofthe inner and outer diameters of the corrugations, can be equal to theinner diameter of the adjoining second pipe section.

[0016] A corrugated section as described above can be manufactured, forinstance, by means of rolling, for metallic materials, injectionmolding, for plastic materials, or winding, for composite material.Apart from the choice of material, the resistance to deformation of thefirst pipe section is decided by the relative axial distance and radialamplitude of the corrugations, as well as the material thickness. Thesevariables are selected with respect to the desired diameter of thepipes, the maximum deformation caused by thermal loading, and thetemperatures and pressures to be handled by the pipes. Deformation ofthe corrugated section in its axial direction will mainly occur duringchanges of temperature in connection with start-up and operation of theplant, while deformation in its radial direction will mainly occurduring assembly and fitting of the pipe joint. By making the pipesection elastically deformable, it will be able to absorb movements inthe same way as a spring. Hence the section will absorb movementsbetween the pipes without transmitting forces to any greater extent. Inorder to enable the deformations, the material thickness of thedeformable first pipe section should be equal to or less than thethickness of the other pipe sections. If the sections have a materialthickness of 1 mm, the corrugated section may have a material thicknessof 0.3-0.6 mm. The selected thicknesses and the relation therebetween isof course dependent on the size of the thermal movements, the dimensionsof the pipes, the pressure of the flowing media and similarly relatedfactors.

[0017] According to a further embodiment, the second pipe section of theinlet pipe has a cylindrical basic shape. The deformable section may beattached to the cylindrical pipe section upstream or downstream relativeto the direction of flow. If the deformable section is placed downstreamof the cylindrical section, then it is directly attached, preferablywelded, to the collection channel going into the heat exchanger. If thepipe assembly includes a further, third cylindrical pipe section, thenthe deformable section may be attached in-between the second and thethird pipe section.

[0018] According to yet a further embodiment, the second pipe sectionhas a conical basic shape. The deformable section may be attached to theconical pipe section upstream or downstream in the direction of flow. Ifthe deformable section is placed downstream of the conical section, thenit is directly attached, preferably welded, to the collection channelgoing into the heat exchanger. The conical pipe section is arranged todiverge in the direction of flow, whereby the diameter of the respectiveinlet and outlet is selected with respect to the flow rate, pressure oroutlet velocity of the flow, and/or other related and desirableparameters.

[0019] According to a further embodiment, the combined inlet and outletpipe joint is made up of two concentric pipes. In this case, the outerpipe joint may either have a cylindrical or conical cross-section. Boththese embodiments of the outer pipe joint can be combined with any oneof the embodiments of the inner pipe joint described above. In thesecases, the average diameter of the corrugated section, as defined above,is preferably equal to the diameters of the adjoining pipe sections.

[0020] The material used for constructing the pipe arrangement is bestchosen with respect to the field of application of the heat exchanger;that is, the type of heat emitting and absorbing medium, and thetemperatures and pressure to which the pipe arrangement will besubjected. High temperatures and pressures will preferably requiremetallic materials, such as steel or aluminum of suitable thickness andquality, while lower temperatures and pressures may allow the use ofplastic pipes. Corrosive media may require particularly resistantmaterials. Joining of metallic pipes is preferably done by welding orsoldering, while plastic materials and composites may be joined bywelding, melting or gluing. Mechanical connections, such as threadedconnections, are also possible, but will at the same time give a morespace consuming, complex and therefore more expensive solution.

BRIEF DESCRIPTION OF DRAWINGS

[0021] In the following description, the invention will be describedwith reference to a number of preferred embodiments, as well as withregard to the attached drawings in which:

[0022]FIG. 1 is a cross-sectional view showing schematically arecuperator, provided with a combined inlet and outlet pipe jointconfigured according to the present invention;

[0023]FIG. 2 is a cross-sectional view showing a pipe connection ofknown configuration;

[0024]FIG. 3 is a cross-sectional view showing an alternative embodimentof the invention; and

[0025]FIG. 4 is a cross-sectional view showing a further alternativeembodiment of the invention.

DETAILED DESCRIPTION

[0026]FIG. 1 shows a schematic representation of a recuperatorcomprising a heat exchanger packet 1 with a combined inlet and outletpipe joint 2, 3, and a outgoing, first collection channel 4 with a pipeconnection 5 between the collection channel and the outlet pipe joint 3.The combined inlet and outlet pipe joint 2, 3 comprises two concentricpipes forming channels for heat transporting media. The inner inlet pipejoint 2 is connected to a source of heat emitting medium, which in thisillustrative case is combusted exhaust gas from a gas turbine which hasnot been shown. The mass flow of heat-emitting medium 6 flows throughthe heat exchanger in which a large portion of its heat energy isemitted to a heat-absorbing medium, which in this case is air. Theheat-absorbing medium is collected in the outgoing, first collectionchannel 4, whereby the flow 7 is directed out through a pipe connection5 to the outlet pipe joint 3 towards the gas turbine. According to thisembodiment, the combined inlet and outlet joint comprises twoconcentric, partially conical channels. The inner pipe section, or theinlet pipe joint 2, is welded to an incoming, second collection channel8 in the form of a diverging section or flange, which in turn isattached to an upper casing 9 on the heat exchanger 1. The upper casing9 conducts the heat-emitting medium in the direction of the flowchannels (not shown) of the heat exchanger. A deformable pipe section 10is attached to the inlet of the inner pipe section 2 and will bedescribed in further detail in connection with FIG. 4 below. The outerpipe section 3 is attached to the flange 8 at its inlet end, facing theheat exchanger, and to a not shown casing surrounding the gas turbine atits opposite end.

[0027]FIG. 3 shows an alternative embodiment of a pipe connection.According to this embodiment, the combined inlet and outlet jointcomprises a pair of concentric, cylindrical inner and outer pipesections 2, 3. The inlet pipe joint 2 includes a deformable,substantially cylindrical, first pipe section 10, attached between acylindrical second pipe section 2 a and a cylindrical third pipe section2 b. The cylindrical second pipe section 2 a is provided with a flange11 for connecting it to a heat source, in this case a gas turbine (notshown), while the cylindrical third pipe section 2 b is welded to theflange 8.

[0028] The deformable first pipe section has an inner diameter, D₁,corresponding to the smallest diameter of the corrugated section 10,which is equal to the inner diameter D₂ of the second section. Hence, inthis case the average diameter D_(M) of the corrugated section is largerthan the inner diameters of the pipe sections. The first pipe section 10is provided with flanges 10 a, 10 b on either side of the corrugatedsection, which flanges are in contact with and welded to the outerperiphery of the second and third section 2 a, 2 b respectively. Duringstart-up of the plant, the temperature of the pipe joint will rise froma relatively low temperature, such as 20° C., to an operatingtemperature in excess of 600° C. The axial movement of the inner pipesection, in connection with thermal expansion of the material, to theextent it differs from that of the outer pipe section, will be taken upby the deformable pipe section 10.

[0029] As may be appreciated from FIG. 3, the outer pipe joint 3 has acylindrical basic shape along its outer periphery. However, it isslightly conical along its inner periphery, as the inner surface iscoated with an insulating material 12 with a gradually increasingthickness. The reason for this is to minimize heat loss from the mediumflowing in the direction of the gas turbine. The conical shape will alsogive certain flow-related advantages.

[0030] The embodiment of FIG. 3 shows a deformable section 10 having acylindrical section 2 a, 2 b on either side. It is, however, possible toeliminate one of these cylindrical sections, whereby the deformablesection is placed at one end of a cylindrical pipe section.

[0031]FIG. 4 shows a further alternative embodiment in the form of apipe connection. According to this embodiment, the combined inlet andoutlet pipe joint comprises a pair of conical inner and outer pipesections 2, 3. The inner pipe section is provided with a deformable,substantially cylindrical first pipe section 10 attached to acylindrical second pipe section. The cylindrical first pipe section isprovided with a flange 11 for connection to a heat source, in this casea gas turbine (not shown), while the conical second pipe section isattached to the flange 8.

[0032] The deformable first pipe section has an inner diameter D₁,corresponding to the smallest inner diameter of the corrugated section,which is equal to the inner diameter D₂ of the adjoining second section.The first pipe section 10 is provided with flanges 10 a, 10 b on eitherside of the corrugated section, which flanges are in contact with andwelded to the outer periphery of the second pipe section 2 and theflange 11, respectively. As can be seen from FIG. 4, the inner surfaceof the outer pipe section is coated with an insulating material with agradually increasing thickness, for reasons stated above (cf. FIG. 3).In this case both the inner and the outer periphery of the outer pipesection has a conical shape. As in the case of the inlet pipe joint, thediameter of the inlet of the outer section is selected with respect tothe flow rate, pressure or outlet velocity of the flow, and/or otherrelated and desirable parameters.

[0033] According to a further alternative embodiment, it is alsopossible to position the deformable first pipe section 10 between theconical second pipe section 2 and the flange 8. Although the diameter D₁of the pipe section 10 will be larger, such a positioning below thelevel of the inlet from the pipe connection 5 will cause lessdisturbance of the flow through the outlet pipe joint 3 as it passes thecorrugations.

[0034] In addition, it is theoretically possible to position thedeformable pipe section 10 between two conical pipe sections 2, in a waycorresponding to that of FIG. 3. However, due to differences in pressurebetween the different channels, as well as forces caused by thermalmovements, the deformable section would be subjected to large stresses.Hence the embodiments described above are preferable.

1. A pipe connection for a heat exchanger (1) in which the heatexchanger comprises a number of corrugated plates, where each plate hasa first edge part opposite a second edge part and a third edge partopposite a fourth edge part, between which corrugated plates there areprovided first and second flow channels, where a heat emitting medium(6) flows through every alternate channel and a heat absorbing medium(7) flows through every other alternate channel, and where a collectingchannel (8) with a diverging cross-section for said heat emitting medium(6) is placed at one side of the heat exchanger and connected to aninlet section a combined inlet and outlet pipe joint (2, 3) for saidheat emitting and heat absorbing media, and an outgoing collectionchannel (4) for said heat absorbing medium (7) arranged on the same sideof the heat exchanger and connected to an outlet section of said inletand outlet pipe joint (2, 3), the inlet pipe joint (2) comprising adeformable first pipe section (10), arranged to absorb thermal andmechanical loading in both axial and radial directions, and at least onefurther, second pipe section (2 a, 2 b).
 2. The pipe connection for aheat exchanger as recited in claim 1, wherein the deformable first pipesection (10) further comprises a substantially cylindrical pipe having acorrugated cross-section in the axial direction of the pipe.
 3. The pipeconnection for a heat exchanger as recited in claim 2, wherein thedeformable first pipe section (10) has an inner diameter (D₁)corresponding to the smallest diameter of the corrugated section, equalto the inner diameter (D₂) of the adjoining second section (2).
 4. Thepipe connection for a heat exchanger as recited in claim 1, wherein thedeformable first pipe section (10) has a material thickness that is lessthan the thickness of the second pipe section.
 5. The pipe connectionfor a heat exchanger as recited in claim 1, wherein the second pipesection (2) has a cylindrical basic shape.
 6. The pipe connection for aheat exchanger as recited in claim 5, wherein the deformable first pipesection (10) is attached to the cylindrical pipe section (2) upstream inthe direction of flow.
 7. The pipe connection for a heat exchanger asrecited in claim 5, wherein the deformable first pipe section (10) isattached to the cylindrical pipe section (2) downstream in the directionof flow.
 8. The pipe connection for a heat exchanger as recited in claim5, wherein the deformable first pipe section (10) is attached betweenthe second, cylindrical pipe section (2 a) and a third, cylindrical pipesection (2 b).
 9. The pipe connection for a heat exchanger as recited inclaim 1, wherein the second pipe section (2) has a conical basic shape.10. The pipe connection for a heat exchanger as recited in claim 9,wherein the deformable first pipe section (10) is attached to theconical pipe section (2) upstream in the direction of flow.
 11. The pipeconnection for a heat exchanger as recited in claim 9, wherein thedeformable first pipe section (10) is attached to the conical pipesection (2) downstream in the direction of flow.
 12. The pipe connectionfor a heat exchanger as recited in claim 1, wherein a combination of theinlet and outlet pipe joint comprises two substantially concentric pipes(2, 3).
 13. The pipe connection for a heat exchanger as recited in claim12, wherein the deformable first pipe section (10) has an inner diameter(D₁) corresponding to the smallest diameter of the corrugated section,equal to the inner diameter (D₂) of the adjoining second section (2).14. The pipe connection for a heat exchanger as recited in claim 12,wherein the outer pipe joint (3) has a conical basic shape.
 15. The pipeconnection for a heat exchanger as recited in claim 1, wherein the inletpipe joint is welded to the incoming collection channel (8).
 16. Thepipe connection for a heat exchanger as recited in claim 1, wherein thedeformable section (10) is welded to the incoming collection channel(8).
 17. A pipe connection for a heat exchanger (1) comprising: twosubstantially concentrically oriented conduits (2, 12) defining two flowchannels, one of said flow channels configured as an annulus about theother; at least one of said conduits (2, 12) comprising a deformablesection (1) for absorbing thermal and mechanical loading in both axialand radial directions when installed on an heat exchanger operating instart-up mode.
 18. The pipe connection for a heat exchanger as recitedin claim 17, wherein the deformable section (10) is configured asbellows corrugations.